Electrophysiological studies will be made of the actions of opiates on single neurones. The principal studies will be made on the opiate sensitive neurones of the myenteric plexus of the guinea-pig ileum, although other studies are in progress using the morphine sensitive neurones in the vas deferens of the mouse and on the vagus nerve. The studies will be made in vitro using both intracellular and extracellar recording techniques. Both the acute actions of opiates and opioid peptides will be studied, as well as the changes which are brought about in these actions by prolonged exposure of the cells to opiate agonists, both in vitro and in vivo. The mechanisms underlying the observed effects will be investigated by changing the ionic content of the perfusing solutions, and by studying the effects of substances which interfere with cyclic nucleotide metabolism and protein synthesis.